Apparatus for exposing photoresist in cylinders

ABSTRACT

A photoresist coating on a cylinder is exposed by placing a mask loosely inside the cylinder and then shining collimated light down the center of the cylinder and onto a conical mirror. The conical mirror reflects the light radially outward through the mask to expose the photoresist on the inner surface of the cylinder. Photoresist on the outside of the cylinder may also be exposed in the same manner by placing a conical mirror around the periphery of the cylinder. To expose the entire length of the cylinder, the conical mirror is moved gradually along the length of the cylinder.

United States Patent [15] 3,645,179 Karol Feb. 29, 1972 [54] APPARATUSFOR EXPOSING 3,080,232 3/1963 Gilbody et al. ..96/36.2 PHOTORESIST INCYLINDERS Primary Examiner-Samuel S. Matthews [72] Inventor. Kenneth N.Karol, Boulder, Colo. Assistant Examiner kichard Sheer [73] Assignee:lntematlonal Business Machines Corpora- AtromeyHanifin and Jancin andHomer L. Knearl tlon, Armonk, NY. 221 Filed: Mar. 27, 1969 [57] ABSTRACTA photoresist coating on a cylinder is exposed by placing a [21] Appl811023 mask loosely inside the cylinder and then shining collimatedlight down the center of the cylinder and onto a conical mir- U-S. onThe conical min-or reflecm the radially outward f GQ PQZ QQM through themask to expose the photoresist on the inner sur- [58] new of Search"95/1, I 1 HC; face of the cylinder. Photoresist on the outside of thecylinder 96/362 may also be exposed in the same manner by placing aconical mirror around the periphery of the cylinder. To expose the en-[Sfil References cued tire length of the cylinder, the conical mirror ismoved gradually along the length of the cylinder.

UNITED STATES PATENTS 2,834,915 5/1958 Dench ..3l5/39.3 8 Claims, 3Drawing Figures PAIENTEDFEB29 m2 SHEET 1 BF 2 FIG. 1

. [6 mv m 5 PR X BY KENNETH '5."

AGENT 3,645,179 1 2 APPARATUS FOR EXPOSING PI-IOTORESIST IN impossible,to place a mask inside a cylinder and insure that CYLINDERSCROSS-REFERENCES TO RELATED APPLICATIONS This invention is a companioninvention to the invention in copending, commonly assigned, patentapplication, Ser. 811,151, entitled Apparatus for Exposing Photoresistin Cylinders, invented by C. G. Speicher, and filed on the same day.

BACKGROUND OF THE INVENTION This invention relates to a method andapparatus for exposing photoresist patterns on the inside and outsidesurfaces of a cylinder. More particularly, the invention relates toexposing photoresist patterns on the surfaces of cylinders by use ofloosely fitting masks and collimated light directed along the radii ofthe cylinder.

In motors used for high-speed feeding of web or tape material, it isdesirable to have a motor armature which has very low inertia. Such anarmature permits the motor rotational direction to change almostinstantaneously from a high forward speed to a high reverse speed. Oneway to obtain an armature with low inertia is to use a cylinder with acircuit printed thereon. The problem then evolves into how tomanufacture a printed circuit cylindrical armature. The cylinder whichmakes up the armature must be very light in weight and yet structurallystrong. These characteristics exist in a cylinder made out ofnonconductive materials, such as fiber glass with conductive coatings onthe inside and outside surfaces. The windings of the armature are formedon the cylinder by use of printed circuit techniques. In the past, threemethods have been utilized to obtain a printed circuit armature.

In one method, the printed circuit is printed and etched in a flatconfiguration as is the typical printed circuit procedure. When thecircuit has been etched, the sheet on which it is etched is then formedinto a cylinder with abutting ends of the sheet being fastened together.This method is not satisfactory because the joint, where the ends of thesheet are fastened together, is not structurally strong enough towithstand the forces on the cylinder when the armature isinstantaneously changed in rotational direction from high-speed forwardto high-speed reverse.

Another method for achieving circuits inside a cylinder is to plate theentire cylinder so that its entire inner surface is coated with anelectrically conductive material. The cylinder is then mounted on amechanical inscribing unit. The inscribing unit utilizes an arm with aneedle mounted on the end thereof to pass inside the cylinder and scrapeaway unwanted portions of the conductive material coated on thecylinder. After the inscribing process is completed a circuitconfiguration is left inside the cylinder.

The inscribing method is not satisfactory because of the mechanicallimitations of inscribing miniature parts. For example, it may benecessary to inscribe the inner wall of the cylinder so as to leave twoconductive paths a few thousandths of an inch apart. It is verydifiicult for a mechanical inscriber to be consistently that accurate.As a result, a great number of armatures are improperly inscribed andmust be rejected as unusable. This is a very wasteful and costly meansof manufacturing armatures.

Accordingly, the ideal method to obtain a circuit in a cylinder would beto coat the inside of the cylinder with a photoresist, place a maskinside the cylinder, expose the mask pattern on the photoresist, and usethe exposed photoresist as a mask for etching a circuit pattern on theinside of the cylinder. The problem herein is that it is not possible touse conventional exposure techniques because the mask cannot be placedsufficiently close to the inside of the cylinder to allow accurateexposure of circuit pattern on the inside of the cylinder.

In the normal photoresist exposure situation, a mask is physically incontact with the photoresist material. Cylinders do not lend themself tothis technique since it is difficult, if not the mask is making goodcontact with the entire inside surface of the cylinder. In addition, ifit were possible to assure good contact with the inside surface of thecylinder, there is the additional problem of how to remove the maskafter the exposure. Also, in a manufacturing process involving largequantities, the procedure for exposing a photoresist must be rapid andeasy to accomplish.

It is an object of this invention to manufacture printed circuitarrnatures in an efl'icient, highly reliable manner with very little orno manufacturing waste due to improper circuit configuration on thearmatures.

It is another object of this invention to expose a photoresist inside aslender cylinder.

It is another object of this invention to expose a photoresist inside oroutside a cylinder without the necessity of having a mask in tightcontact with the walls of the cylinder.

SUMMARY OF INVENTION In accordance with the above objects, the inventionis accomplished by placing a mask loosely inside a cylinder whose insidesurface is coated with photoresist. Collimated light is then directedinto the cylinder with its beams being substantially parallel to theaxis of a cylinder. The light beams are reflected by a conical mirrorinside the cylinder with the axis of the conical mirror lying on theaxis of the cylinder. Light reflected from the conical mirror isradially collimatedcollimated in radial planes and passes through themask to expose the photoresist on the inside surface of the cylinder.

As another feature of the invention, the conical mirror is moved alongthe entire length of the cylinder to expose the entire cylinder. If theconical mirror is as long as the cylinder, then it need not be moved.

As another feature of the invention, a photoresist on the outsidesurface of the cylinder may be exposed by placing a mask loosely aroundthe cylinder and using an outside conical mirror whose axis also lies onthe axis of the cylinder. This mirror reflects the collimated lightradially in toward the outside surface of the cylinder.

The great advantage of this invention is that the inner or outer maskmay be loosely mounted relative to the cylinder whose photoresist isbeing exposed. The accuracy of the pattern printed on the photoresist,by exposure through the masks, will be preserved by use of nondivergentlight which is moving along a radius of the cylinder. Thus, a truepattern with clear and distinct edges will be exposed in thephotoresist.

Another advantage of the invention is that by having the cylinderand-masks loosely mounted relative to each other, the cylinder may berapidly removed from the masks after the exposure is completed.

Another advantage of the invention is that the structural integrity ofthe armature is preserved since it is one continuous piece. The armatureis much stronger than if it were a flat piece rolled and bonded to forma cylinder. As one continuous piece, the cylinder is better able towithstand forces it will later encounter when used in a motor.

Still another advantage of the invention is that by using a mask andphoto exposure method to print the circuit on the cylinders, the size ofthe printed circuit paths and their separation on the cylinder can be assmall as desired-down to thousandths of an inch. Also, the circuitpattern can have paths in any direction since the light is normal to themask as it strikes the mask.

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of a preferred embodiment of the invention, as illustratedin the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 shows the preferred embodiment ofthe invention wherein the photoresist on the surfaces of the cylinder isbeing exposed.

FIG. 2, taken along lines 2-2 of FIG. 1, shows a cross-section of themasks and cylinder and the relative position of the inner and outerconical mirrors to the cylinder.

FIG. 3, taken along lines 3-3 of FIG. 1, shows a top view looking downinto the cylinder with a cutaway of the cylinder so that the cylinderandmask'may be seen edge on.

DESCRIPTION In FIG. 1, the cylinder to be exposed is placed inside themask 10. A cap 12 is placed on top of the mask-cylinder-mask structureto prevent light from striking the end edges of the masks and thecylinder. The source of light is a collimator assembly 14 at the top ofthe drawing. The collimator assembly 14 is made up of a mercury arc lampand collimating lenses. This combination will produce a bright,substantially non divergent light beam. A mercury arc lamp is usedbecause it produces strong ultraviolet light, and the photoresist usedis responsive to ultraviolet light. Of course, other photoresists andlight sources matched to the photoresist could be used.

Light from the collimator assembly, 14 passes down through the hole 16and into the chamber where the masks and cylinder are located. Thecollimated light from collimator assembly 14 passes through the hole 16and strikes the inner conical mirror 18. The light reflects off themirror and moves radially outward until it strikes either the mask orpasses through the mask and strikes the inside surface of the cylinder.

The collimated light also passes along the outside of the mask andstrikes the conical mirror 20. The mirror 20 reflects the light radiallyin toward the mask 10 and the outer surface of the cylinder. Lightreflected off the conical mirror 20 will either strike the mask 10 orwill be passed by the mask 10 to impinge on the outer surface of thecylinder.

In order to expose the entire cylinder, the inner conical mirror l8 andthe outer conical mirror 20 are moved along the length of the cylinder.The movement is hydraulically actuated by hydraulic device 22 and isguided by the rods 24 passing through fixed plates 26 and 28. The plates26 and 28 are a part of the box 30 which provides the light-tightchamber in which the cylinders are exposed. Access to the chamber is viadoor 32 which contains a dark glass window 34. The box 30 also serves assupport for the collimator 14 which is fixedly mounted on the box.

Control of the exposure operation is provided by control box 36 whichhas electrical circuits for controlling operation of the collimator 14,the hydraulic device 22 and the shutter solenoid 38.

The shutter solenoid 38 operates to move the shutter 40 over the opening16 before and after the exposure operation.

The position of the cylinder relative to the masks and mirrors may bemore clearly seen in FIGS. 2 and 3. In FIG. 2, the outer mask 10 isshown in immediate proximity to the cylinder 42 and the inner mask 44.Cap 12 is shown at the top of FIG. 2 in position over the masks andcylinder. In FIG. 2 the masks and cylinder are shown in contact. If thedrawing were greatly enlarged, it would be clear that there is spacingof a few hundredths to a few thousandths of an inch between the outersurface of the cylinder and mask 10 and also between the inner surfaceof the cylinder 42 and the mask 44. Thus, the cylinder 42 may be easilyinserted or removed by sliding between the two masks 10 and 44.

The outer mask 10 and the inner mask 44 are seated in the base plate 26.The cylinder is placed in the apparatus for exposure by sliding it downbetween the two masks. Thereafter, the cap 12 is placed on top of thecylinder and mask so as to prevent light from impinging on the upperedge of the masks and cylinder.

In FIG. 2 the inner conical mirror 18 and the outer conical mirror 20are shown in a position about half way along the length of the cylinder.The mirrors l8 and 20 may be any polished surface which will reflect thelight radially toward the masks and cylinder. Mirror 18 is physicallymounted on the end of piston 25, while mirror 20 is carried on aplatform 29 physically attached to the end of rods 24. As piston ispushed upward by the hydraulic device 22 (FIG. 1), platform 29 is alsocarried upwarduOf course, the direction in which the mirrors move duringexposure-from top to bottom or from bottom to top-is not critical to theexposure of the photoresist on the cylinder. Either direction wouldprovide an operative method of exposure. The piston 25 and the rods 24are allowed to slide through the platform 26 by the bearings 46. 1

As shown in FIG. 2, light beams arriving at the top of FIG. 2 in adirection parallel to the axis of the cylinder strike the conical mirror18 and are reflected radially out toward the mask 44 and the innersurface of the cylinder 42. Similarly,

light rays parallel to the axis of the cylinder 42- pass along theoutside of the mask 10, strike the mirror 20 and are reflected radiallyin toward the mask 10 and the outer surface of the cylinder 42.

In FIG. 3, the radial direction of the light beams 47 as they move fromthe mirrors 18 and 20 to the cylinder 42 is shown.

OPERATION Referring again to FIG. 1, a photoresist coated cylinder maybe placed-into position for exposure by removing the cap 12 and slidingthe cylinder down between the outer mask I0 and the inner mask 44 (FIG.2). With the door 32 closed and the shutter 40 over the opening 16, thechamber then is relatively light-tight.

To initiate operation, the operator flicks the light switch 50 whichturns on the mercury arc in collimator assembly 14. After a shortinterval during which the collimator white light source warms up andproduces a beam of the full intensity, the operator then presses thestart button 52. The start command causes the hydraulic device 22 toraise the mirrors 18 and 20 to the top of the cylinder. A microswitch,which is a part of hydraulic device 22 and is not shown, signals thecontrol box 36 when the mirrors are at the top of the cylinder. Thecontrol box 36 then actuates the solenoid 38, which swings the shutter40 away from the opening 16. The collimated light then passes downthrough the-opening 16 to begin the exposure sequence.

During exposure the hydraulic device 22 slowly lowers the mirrors l8 and20. The rate at which the mirrors are lowered may be controlled byrotating control dial 54. This effectively adjusts the time of exposure.When the mirrors reach the bottom of the cylinder, another microswitch,which is also a part of the hydraulic device 22, senses the mirrorposition and signals the control box 36 that the exposure is complete.The control box 36 in turn deactivates the solenoid 38. The shutter 40then closes over the opening 16.

The cylinder may then be removed by lifting cap 12 and sliding thecylinder from between the masks.

It will be obvious to one skilled in the art that there are manyvariations in mounting hardware and control hardware which might be usedto implement the invention. However, the gist of the invention is in theuse of collimated light with conical mirrors to convert the light intoradially collimated beams. The radial beams pass through masks to theinner or outer surface of a cylinder to expose a very accurate patternin a photoresist. Of course, the size of the cylinder exposed isimmaterial.

While the invention has been particularly shown and described withreference to a preferred embodiment thereof, it will be understood bythose skilled in the art that the foregoing and other changes in formand details may be made therein without departing from the spirit andscope of the invention.

What is claimed is:

1. Apparatus for exposing a pattern in a photoresist layer coated on acylinder comprising:

means for masking light beams whereby a shadow pattern is projected ontothe photoresist layer, said means mounted adjacent to, but not attachedto, the photoresist layer on the inside surface of the cylinder so thatthe cylinder is slidable relative to said masking means;

a source of collimated light positioned for directing collimated lightinside the cylinder and parallel to the axis of the cylinder;

means positioned inside the cylinder for reflecting the collimated lightradially outward so that the light travels along the radii of thecylinder to pass through said masking means and expose a pattern in thephotoresist layer on the inside surface of the cylinder.

2. The apparatus of claim 1 wherein said masking means comprises acylindrical, optical mask positioned loosely inside the cylinder.

3. The apparatus of claim 1 wherein said reflecting means is a conicalmirror with the axis of the cone positioned on the axis of the cylinder,and with the cones outside surface being the reflecting surface.

4. The apparatus of claim 3 and, in addition:

means for moving the conical mirror along the length of the cylinder toexpose the photoresist on the entire inside surface of the cylinder.

5. The apparatus of claim 1 and, in addition:

second means for masking light beams whereby a shadow pattern may beprojected onto the photoresist layer, said second masking means mountedadjacent to, but not attached to, the photoresist layer on the outsidesurface of the cylinder so that the cylinder is slidable relative tosaid second masking means;

said source also positioned for directing the collimated light outsidethe cylinder and parallel to the axis of the cylinder;

means positioned outside the cylinder for reflecting the collimatedlight radially inward so that the radiant energy travels along the radiiof the cylinder in toward said second masking means and exposes apattern in the photoresist layer on the outside surface of the cylinder.

6. The apparatus of claim 5 wherein said second masking means comprisesa cylindrical optical mask positioned loosely outside the cylinder.

7. The apparatus of claim 5 wherein said reflecting means positionedoutside the cylinder is a conical mirror with the axis of the conepositioned on the axis of the cylinder, and with the cones insidesurface being the reflecting surface.

8. The apparatus of claim 7 and, in addition, means for moving theoutside conical mirror along the length of the cylinder to expose thephotoresist layer on the entire outside surface of the cylinder.

1. Apparatus for exposing a pattern in a photoresist layer coated on acylinder comprising: means for masking light beams whereby a shadowpattern is projected onto the photoresist layer, said means mountedadjacent to, but not attached to, the photoresist layer on the insidesurface of the cylinder so that the cylinder is slidable relative tosaid masking means; a source of collimated light positioned fordirecting collimated light inside the cylinder and parallel to the axisof the cylinder; means positioned inside the cylinder for reflecting thecollimated light radially outward so that the light travels along theradii of the cylinder to pass through said masking means and expose apattern in the photoresist layer on the inside surface of the cylinder.2. The apparatus of claim 1 wherein said masking means comprises acylindrical, optical mask positioned loosely inside the cylinder.
 3. Theapparatus of claim 1 wherein said reflecting means is a conical mirrorwith the axis of the cone positioned on the axis of the cylinder, andwith the cone''s outside surface being the reflecting surface.
 4. Theapparatus of claim 3 and, in addition: means for moving the conicalmirror along the length of the cylinder to expose the photoresist on theentire inside surface of the cylinder.
 5. The apparatus of claim 1 and,in addition: second means for masking light beams whereby a shadowpattern may be projected onto the photoresist layer, said second maskingmeans mounted adjacent to, but not attached to, the photoresist layer onthe outside surface of the cylinder so that the cylinder is slidablerelative to said second masking means; said source also positioned fordirecting the collimated light outside the cylinder and parallel to theaxis of the cylinder; means positioned outside the cylinder forreflecting the collimated light radially inward so that the radiantenergy travels along the radii of the cylinder in toward said secondmasking means and exposes a pattern in the photoresist layer on theoutside surface of the cylinder.
 6. The apparatus of claim 5 whereinsaid second masking means comprises a cylindrical optical maskpositioned loosely outside the cylinder.
 7. The apparatus of claim 5wherein said reflecting means positioned outside the cylinder is aconical mirror with the axis of the cone positioned on the axis of thecylinder, and with the cone''s inside surface being the reflectingsurface.
 8. The apparatus of claim 7 and, in addition, means for movingthe outside conical mirror along the length of the cylinder to exposethe photoresist layer on the entire outside surface of the cylinder.